U.S. patent number 4,822,058 [Application Number 07/103,151] was granted by the patent office on 1989-04-18 for radial lip seal.
This patent grant is currently assigned to Federal-Mogul Corporation. Invention is credited to John D. Butler, Jon A. Chandler.
United States Patent |
4,822,058 |
Butler , et al. |
April 18, 1989 |
Radial lip seal
Abstract
A radial lip seal (10) having a sealing lip (16) made of first
and second materials arranged in alternating regions (20,22) and
forming a continuous contact band. The seal is a rotational seal
for contacting a shaft or sleeve in a relatively rotatable
relationship. The first and second materials have differing
physical characteristics to increase hydrodynamic activity at the
sealing lip (16). The first material may be a
polytetrafluoroethylene material and the second material disclosed
may be silicone, fluoroelastomer, nitrile, ethylene acrylic or
polyacrylate elastomers. The boundaries (42) between the first and
second materials at the contact band preferably intersect the
circumferentially extending contact band at an angle. A method of
making a radial lip seal is also disclosed wherein an annular wafer
(32) of a first material having an undulating circumferential edge
(34) with spaced radially recessed portions (36) is placed in a
mold (44). A ring (45) of elastomeric material is placed in the
mold (44) with the wafer (32). The radial lip seal (10) is then
formed by molding the ring (45) of elastomeric material and wafer
(32) into the desired seal configuration. The process is completed
by forming the sealing lip (16) by cutting the molded wafer (32)
and molded elastomeric material contained in the recesses (36) of
the wafer (32).
Inventors: |
Butler; John D. (Van Wert,
OH), Chandler; Jon A. (Brighton, MI) |
Assignee: |
Federal-Mogul Corporation
(Southfield, MI)
|
Family
ID: |
22293661 |
Appl.
No.: |
07/103,151 |
Filed: |
October 1, 1987 |
Current U.S.
Class: |
277/559; 277/565;
277/569; 277/575; 277/922; 277/924; 264/138 |
Current CPC
Class: |
F16J
15/328 (20130101); B29D 99/0053 (20130101); F16J
15/3244 (20130101); Y10S 277/922 (20130101); B29L
2031/26 (20130101); Y10S 277/924 (20130101) |
Current International
Class: |
B29D
31/00 (20060101); F16J 15/32 (20060101); F16J
015/32 (); B29C 017/10 () |
Field of
Search: |
;264/138,277 ;29/451,460
;384/482-486,300,151-153,147
;277/1,42,65,75,80,152,153,134,164,228 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Griffin; Donald A.
Attorney, Agent or Firm: Shurupoff; Lawrence J. Hess; Robert
F.
Claims
What is claimed is:
1. A rotational contact seal comprising:
an annular sealing member having a lip for contacting a relatively
rotatable shaft;
said lip formed of a first material and a second material, said
first and second materials having different material properties and
defining a continuous circumferentially extending contact band
having alternating first and second separate regions formed of the
first and second materials respectively.
2. The rotational contact seal of claim 1 wherein the first
material is harder than the second material.
3. The rotational contact seal of claim 1 wherein the first
material has a lower coefficient of friction than the second
material.
4. The rotational contact seal of claim 1 wherein said first and
second regions have distinct boundaries extending at an angle
relative to the lip.
5. The rotational contact seal of claim 4 wherein the boundaries of
the first region between said first and second regions converge
from a point on a non-fluid side of the lip to the lip and diverge
from a point on a fluid side of the lip to the lip.
6. The rotational contact seal of claim 5 wherein the first
material is polytetrafluoroethylene.
7. The rotational contact seal of claim 5 wherein the second
material is selected from the group of elastomers consisting of:
silicon, fluoroelastomer, polyacrylate, ethylene acrylic and
nitrile.
8. The rotational contact seal of claim 5 wherein said first
material has a preselected modulus of elasticity and said second
material has a lower modulus of elasticity than said first
material.
9. An oil seal comprising:
an annular case;
a sealing annulus formed of elastomeric material bonded to an inner
diameter of the case, said sealing annulus having a sealing lip
formed thereon having a diameter smaller than the inner diameter of
the case; and circumferentially spaced portions formed of
polytetrafluoroethylene forming part of the sealing lip with the
elastomeric material being disposed between the spaced portions to
provide a sealing lip formed of alternating elastomeric material
and polytetrafluoroethylene material.
10. The rotational contact seal of claim 9 wherein said elastomeric
material and polytetrafluoroethylene material have distinct
boundaries extending at an angle relative to the sealing lip.
11. The rotational contact seal of claim 10 wherein the boundaries
of the polytetrafluoroethylene material between said elastomeric
material and said polytetrafluoroethylene material converge from a
point on an air side of the sealing lip to the sealing lip and
diverge from a point on a fluid side of the sealing lip to the
sealing lip.
12. The rotational contact seal of claim 9 wherein the elastomeric
material is selected from the group of elastomers consisting of:
silicone, fluoroelastomer, ethylene acrylic, polyacrylate and
nitrile.
13. A method of making an oil seal comprising:
forming an annular wafer of a first material having an undulating
circumferential edge with circumferentially spaced radially
recessed portions;
placing said wafer and a ring of a second material in a mold;
molding the wafer and ring to a predetermined shape with the second
material flowing into the recessed portions of the wafer;
bonding the first and second materials together; and
trimming a sealing lip by circumferentially cutting the molded
wafer and second material contained in the recessed portions.
14. The method of claim 13 wherein said first material is
polytetrafluoroethylene and the second material is an
elastomer.
15. In the method of claim 14 wherein the step of forming the
annular wafer is followed by the steps of:
etching the surface of the wafer; and
applying an adhesive coating to the wafer.
16. The method of claim 13 wherein the wafer and ring are
concentrically located by placing said wafer and said ring adjacent
a cylindrical wall of the mold.
17. The method of claim 13 further comprising the step of locating
a case in the mold with the wafer and the ring and bonding the
second material to the case.
18. The method of claim 13 further comprising the step of forming a
second lip axially spaced from the sealing lip, said second lip
being integrally molded from the second material.
Description
TECHNICAL FIELD
This invention relates to a radial lip seal for sealing with a
relatively rotatable cylindrical member. The invention has
particular utility in the automotive and heavy equipment industries
for crankshaft seals, transmission seals, and wheel bearing
seals.
BACKGROUND ART
Hydrodynamic radial lip seals have been developed to improve
performance and durability of rotational contact seals.
Radial lip seals used in relatively rotatable applications are
inherently hydrodynamic to a limited extent. Hydrodynamic activity
can be increased by incorporating special hydrodynamic aids such as
grooves, flutes, ribs or threads adjacent the sealing lip. As seal
lips having hydrodynamic aids are rotated, the aids act as small
hydrodynamic pumps that direct fluid in contact with the seal lip
to the fluid side of the lip. Hydrodynamic elements must be
carefully formed and properly installed to be effective.
Hydrodynamic seals are sensitive to eccentricity of the shaft or
sleeve. If the seal is eccentric relative to the element against
which it seals, hydrodynamic activity may be substantially
reduced.
Polytetrafluoroethylene (PTFE) has been proposed as a seal material
for rotational contact seals. While hydrodynamic elements may be
molded or cut on a PTFE seal lip, frictional wear tends to rapidly
neutralize the effect of the hydrodynamic aids.
PTFE wafers are also used as sealing elements by deforming the
wafers into a conical configuration. In the conical configuration
the PTFE wafer is held with a substantial interference fit against
the relatively rotated machine element. PTFE seals having a conical
configuration must be carefully installed to prevent scoring the
PTFE wafer.
One advantage of PTFE seals is that imperfections in the surface
contacted by the seal element may be filled by PTFE being deposited
in grooves or indentations. This smooths the surface sealed and
tends to improve seal life.
While hydrodynamic seals have improved seal life and performance
when properly manufactured and installed, a simple and effective
hydrodynamic seal that is easy to manufacture and install has long
been needed to permit the use of hydrodynamic seals in conventional
and innovative seal applications.
DISCLOSURE OF INVENTION
An object of the present invention is to provide an improved
bi-directional hydrodynamic seal that is easy to manufacture and
install.
Another object is to provide a durable hydrodynamic seal which
features a seal lip providing the benefits of the use of a
fluoroelastomer or PTFE material in an alternating array with a
second material having different physical characteristics.
The rotational contact seal of the present invention comprises a
sealing annulus having a sealing lip which contacts a relatively
rotatable shaft or sleeve. Hereinafter, references to the machine
element contacted by the seal lip will be simplified by referring
to the machine element as a shaft. However, it should be understood
that the seal of the present invention may be used as an inner
diameter or outer diameter seal. The sealing lip of the seal is
formed of first and second materials having different physical
characteristics. The first and second materials form a continuous
circumferentially extending contact band having alternating first
and second regions formed of the first and second materials
respectively.
The first and second materials may differ in material
characteristics relating to their hardness, coefficient of friction
or modulus of elasticity. The first material is preferably PTFE.
The second material is preferably an elastomer such as silicone,
fluoroelastomer, nitrile, ethylene acrylic or polyacrylate.
The boundaries, or edges, of the first regions between the first
and second regions at the seal lip extend at an angle relative to
the circumferentially extending contact band. In the preferred
embodiment, the boundaries of the first regions between the first
and second regions converge radially inwardly from a point on the
air side of the contact band to the contact band and diverge
radially inwardly from a point on the fluid, or oil, side of the
contact band to the contact band.
Shaft oil seals of the present invention preferably include a rigid
annular case bonded to a sealing annulus of elastomeric material.
The sealing annulus has a sealing lip with a diameter smaller than
the inner diameter of the case. An annular wafer used to form part
of the sealing lip includes spaced portions between which the
elastomeric material of the sealing annulus is deposited. The
sealing lip is preferably formed by circumferentially trimming the
annular wafer at the recesses providing a continuous sealing lip
formed of alternating elastomeric material and PTFE.
The method of the present invention comprises forming an annular
wafer of a first material. The annular wafer has an undulating
circumferential edge having either spaced radially recessed
portions or spaced radially extending portions. The wafer is placed
in a mold for forming a seal with a ring of a second material. The
wafer and ring are then molded to the desired seal configuration.
During the molding operation, the ring of elastomeric material
flows into the recessed portions or between radially extending
portions of the wafer as the wafer and elastomeric material are
bonded together. The seal is completed by circumferentially
trimming a sealing lip by alternately cutting the molded wafer and
the portion of the second material contained in the recesses or
between the radially extending portions of the wafer.
The first material is preferably a PTFE material or the like and
the second material is preferably an elastomer. When using a PTFE
wafer it is generally necessary to include the further steps of
etching the surface of the wafer and applying an adhesive coating
to the wafer prior to the molding operation.
The wafer and ring are located within the mold by placing the wafer
and ring adjacent to a cylindrical wall of the mold which holds
them concentrically in the mold.
The method may also include the step of locating an annular case
within the mold when the mold is loaded with the wafer and the
ring. The ring is bonded to the annular case during the molding
step.
The molding step may also include the step of forming one or more
auxiliary lips on the seal spaced from the sealing lip. The
auxiliary lip is preferably integrally molded from the second
material.
The objects, features and advantages of the present invention are
readily apparent from the following detailed description of the
best mode for carrying out the invention when read in view of the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a perspective view of a radial lip seal formed in
accordance with the present invention.
FIG. 2 is a perspective view of a radial lip seal in accordance
with the present invention.
FIG. 3 is a cross-sectional view taken on along the line 3--3 in
FIG. 2.
FIG. 4 is a cross-sectional view taken along the line 4--4 in FIG.
2.
FIGS. 5 through 10 are plan views of annular wafers use in forming
radial lip seals in accordance with the present invention.
FIG. 11 is a perspective view of a radial lip seal formed in
accordance with the present invention.
FIG. 12 is a fragmentary perspective view of a portion the sealing
lip of a radial lip seal made in accordance with the present
invention.
FIG. 13 is a one-half section view of a seal mold loaded with an
annular wafer, a ring of elastomeric material, and a case.
FIG. 14 is a fragmentary cross-sectional view of the seal mold of
FIG. 13 in the initial phase of the molding operation.
FIG. 15 is a fragmentary cross-sectional view of the seal mold of
FIG. 13 as the ring of elastomeric material is formed around the
annular wafer.
FIG. 16 is a fragmentary cross-sectional view of the seal mold of
FIG. 13 showing the seal fully molded.
FIG. 17 is a cross-sectional view of a seal with a knife
diagrammatically shown illustrating the step of trimming the
sealing lip.
BEST MODE FOR CARRYING OUT THE INVENTION
Referring now to FIGS. 1 and 2, two different embodiments of the
radial lip seal 10 of the present invention are shown. The seal 10
includes a case 12 which is preferably a metal annular member used
to support and install the seal. An elastomeric annulus 14 is
bonded to the case 12. A sealing lip 16 and an auxiliary lip 18 are
formed as part of the elastomeric annulus 14. The sealing lip 16
includes first and second regions 20, 22 formed of first and second
materials respectively having different physical characteristics.
The sealing lip 16 has a fluid side 24 and an air side 26. The
fluid, or oil, side 24 is that side of the sealing lip 16 which
faces a fluid reservoir from which the seal is intended to prevent
fluid leakage. The air side 26 is that side of the sealing lip 16
from which the fluid contained by the seal is excluded. A waste
ring 28, or offal, which is trimmed from the seal 10 after molding
is shown in FIGS. 1 and 2 to illustrate how the seal is trimmed to
provide a seal having a sealing lip 16 formed of alternating first
and second regions 20, 22.
Referring now to FIGS. 3 and 4, two cross-sections of the seal 10
are shown to illustrate the structure of the sealing lip 16 as it
changes about the inner circumference of the seal. In FIG. 3 the
sealing lip 16 is formed of the elastomeric material forming the
second region 22. In FIG. 4 the sealing lip 16 is formed of the
material forming the first region 20. In FIG. 3 the first region 20
forms no part of the sealing lip 16 on either the fluid side 24 or
the air side 26 of the sealing lip 16. In FIG. 4 the first region
20 forms both the fluid side 24 and air side 26 of the sealing lip
16.
A garter spring groove 30 is shown in both FIGS. 3 and 4 radially
outwardly spaced from the sealing lip 16. A garter spring, not
shown, may be installed in the garter spring groove 30 to provide
an inward biasing force on the sealing lip 16 as is well known in
the art.
Referring now to FIGS. 5 through 10 different alternative
configurations of the wafer used in forming the seal of the present
invention are shown. The wafer includes an undulating edge that may
form the inner diameter or outer diameter of the wafer. The
circular edge 35 of the wafer is adapted to be piloted on a
cylindrical surface of the mold used to form the seal. A trim line
T is shown in each of FIGS. 5 through 10 in dashed lines to
indicate the approximate area that each wafer will be trimmed after
molding.
FIG. 5 shows a wafer ring having an inner diameter undulating edge
34 comprising three recesses 36.
FIG. 6 shows a wafer ring 32 having an inner diameter undulating
edge 34 comprising twelve recesses 36. The recesses 36 are distinct
and separate crescent shaped recesses separated by protrusions 38
comprising a series of arcuate segments defining a notched circular
inner diameter. A seal made with a similarly shaped wafer is
illustrated in FIG. 2.
FIG. 7 shows an alternative form of the wafer ring 32 having an
inner diameter undulating edge 34. Eight recesses 36 are separated
by eight protrusions 38. The protrusions 38 of the illustrated
embodiment comprise sections of a circular inner diameter. The
recesses 36 define sections of a diameter intermediate the diameter
of the protrusion 38 and the outer diameter of the wafer ring 32.
Ramp surfaces 39 interconnect the recesses 36 and protrusions
38.
In FIG. 8 a wafer ring 32 having an outer diameter defined by an
undulating edge 34 is shown. The recesses 36 are formed by straight
line segments intersecting at an oblique angle between adjacent
protrusions 38.
FIG. 9 shows an alternative embodiment of the wafer ring 32 having
an outer diameter undulating edge 34. The undulating edge 34 is
formed by twelve recesses 36 having a crescent shape. The recesses
36 are spaced about the circumference of the wafer ring 32 by
protrusions 38. The seal illustrated in FIG. 1 is representative of
a seal made with a similarly shaped wafer ring 32. The first
regions 20 in FIG. 1 are trimmed off protrusions 38 of the wafer
ring 32.
Referring now to FIG. 10, an integrally formed wafer ring 32 is
shown which has an outer diameter undulating edge 34 that is
specially contoured in the irregular configuration substantially as
shown. The undulating edge 34 is formed by five protrusions 38.
Slots 40 converge on opposite sides of the protrusions 38 to
separate the recesses 36 from the protrusions. This type of wafer
ring 32 is shown incorporated in a seal in FIGS. 11 and 12. The
wafer ring is trimmed radially outward of the recessed portions 34
so that the protrusions 38 are separated from the ring. Protrusions
38 are left as discrete regions 20 on the finished seal having
specially oriented boundaries as described below. This wafer design
has produced the best hydrodynamic performance in testing.
Referring now to FIGS. 11 and 12, the sealing lip 16 of a seal 10
molded in accordance with the present invention is shown in greater
detail. The sealing lip 16 includes first and second regions 20 and
22 which are separated by a distinct boundary 42. The boundary 42
is believed to improve the hydrodynamic effect achieved by the seal
10 without the use of grooves or other hydrodynamic aids. The
sealing lip 16 is a continuous lip having no conventional
hydrodynamic elements that may be worn away. Rotation of the
sealing lip 16 relative to a shaft creates the desired hydrodynamic
effect.
As best shown in FIG. 12, the boundaries 42 of the first region 20
converge at an angle A relative to a radial line from the air side
26 of the seal to the sealing lip 16. On the fluid side 24 of the
sealing lip 16 the boundaries 42 of the first region 20 diverge at
an angle B relative to a radial line.
It is believed that the boundary 42, even though formed as a
continuous surface, acts as vane which may create a fluid pressure
differential for pumping fluid back toward the fluid side of the
seal. The difference in the physical characteristics of the
materials forming the first region and the second region are
believed to improve the hydrodynamic performance of the seal.
The material of the first region 20 may have a lower coefficient of
friction, greater hardness, or a lower modulus of elasticity than
the second region 22. The difference in hardness or coefficient of
friction between the material forming the first region 20 and the
second region 22 may create a pressure differential across the
boundary.
It has been determined in some instances that the extent that the
boundary 42 is angled relative to the sealing lip may enhance or
reduce the hydrodynamic effect.
Referring now to FIGS. 13-17, the method of forming a seal 10 in
accordance with the present invention will be described in detail.
In FIG. 13 a mold 44 is shown with a case 12, wafer ring 32 and a
prep ring 45 loaded in the lower half of the mold 44. The prep ring
45 is formed of substantially uncured elastomeric material such as
a silicone, polyacrylate, fluoroelastomer, ethylene acrylic, or
nitrile elastomer. The wafer ring 32 is preferably formed of PTFE
but may also be formed of another fluoroelastomer or natural
rubber. It is important that the physical characteristics of the
wafer 32 and the prep ring 45 differ from each other. As shown in
FIG. 13, the upper half 48 of the mold is disengaged from the lower
half 46 for loading.
Referring now to FIG. 14, the molding operation is commenced by
moving the upper half 48 of the mold toward the lower half 46. The
prep ring 45 and wafer ring 32 are concentrically located upon a
cylindrical surface 52 in the lower half 46 of the mold 44. The
cylindrical surface 52 keeps the wafer ring 32 and prep ring 45
concentrically located within the mold throughout the molding
operation. As the upper half 48 moves towards the lower half 46,
the prep ring 45 is contacted by the upper half 48 of the mold 44.
The mold 44 is heated to melt and cure the prep ring 45.
Referring now to FIG. 15, the prep ring 45 is deformed to fill the
mold cavity formed by the upper and lower halves 48, 46. The
elastomeric material of the prep ring 45 flows into the recesses 36
of the wafer and throughout the mold cavity.
Referring now to FIG. 16, the molding operation is completed when
the elastomeric material of the prep ring 45 completely fills the
cavity between the upper and lower halves 44 and the elastomeric
material is substantially cured. A flange 54 of the case 12 is
preferably cold formed at the inner edge of the case 12 as the mold
is closed. The elastomeric material of the prep ring 45 flows
around and is bonded to the flange 54 of the case 12. The outer
portion of the wafer ring 32 is forced downwardly by the flow of
the elastomeric material of the prep ring 45 and formed into a
frustoconical shape. One side of the frustoconical portion of the
wafer ring 32 may form the air side 26 of the sealing lip 16.
Referring now to FIG. 17, the trimming step is illustrated
diagrammatically by a knife which trims the seal through the
elastomeric material in the recesses of the wafer ring and through
the wafer ring 32. A continuous sealing lip 16 is formed by the
trimming operation. Sealing lip 16 includes both the first and
second regions 20 and 22 in a sequentially alternating pattern. The
circular web of the wafer ring 32 may be trimmed off with the waste
ring 28 as shown in FIG. 1 or included as part of the air side 26
of the sealing lip 16 as shown in FIG. 2.
While the best mode for carrying out the invention has been
described in detail, those familiar with the art to which this
invention relates will recognize alternative ways of practicing
this invention as defined by the following claims.
* * * * *